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Topic: [SOLVED] Wrong connection to a 74HC595 Shift Register ? (Read 1 time) previous topic - next topic

retronet_RIMBA1ZO

Jan 13, 2014, 07:08 am Last Edit: Jan 14, 2014, 05:49 am by retronet_RIMBA1ZO Reason: 1
Was trying to be a smarty pants by saving jumper wires in the following;

Regarding the wires to ground, instead of connecting each of pins 8 & 13 to GND, would it not be the same thing to connect 8 to 13 (A to B in the diagram) and skip using the wire at 'C' ?
Or does this "short" something in the chip ?

I've already done the same with the 3V3 lines and it works - i bridge 16 to 10 and then just one wire to the Arduino.

(If it's relevant, the rest of the diagram is just the Project 14 layout in the Earthshine Turorial "Shift Register 8-Bit Binary Counter")

TomGeorge

Hi, yes you can, it just makes debugging a protoboard a bit hard, but in  this case with small currents it will be fine.

Tom...... :)
Everything runs on smoke, let the smoke out, it stops running....

Grumpy_Mike

Yes that sort of wiring is known as chaining. The only problem is that when you chain too much you have to add extra decoupling capacitors to the power supply.

I notice you haven't got any at all!

MarkT

0.1uF ceramic decoupling capacitor on each logic chip is recommended practice,
right up close to the chip.

On a breadboard that's a little awkward, but you can put it between the power rails.

I note you are using ground on the bottom pair of rails, +5V on the top pair.  That's
not ideal way to do it - use a single pair of rails, then the decoupling caps
can simply be on that pair.  Keep power and ground close together to avoid big loops
and their stray inductance.

If you are switching lots of LEDs then decoupling is very important as you are switching
perhaps 100's of mA at nanosecond timescales - I would recommend both 0.1uF per chip
and 10uF to 100uF per breadboard.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

retronet_RIMBA1ZO


Hi, yes you can, it just makes debugging a protoboard a bit hard, but in  this case with small currents it will be fine.

Tom...... :)

OK, that means i'll have to check the wiring contacts again because it doesn't seem to work with the "shortcut".

Thanks to Mark & Mike on the capacitor tips, this is just working through n00b tutorials on Arduino so it probably doesn't delve too much into the detailed electronic basics which i'm not quite familiar with, so pointers into "best practice" is always appreciated.

Actually Mike, i believe i've viewed your site with it's highlight of Power Supply decoupling - i was actually linked to read the State Machine section (very nicely explained, THANKS SO MUCH) and then worked back from the beginning. GREAT SITE !!

Grumpy_Mike

Thanks for you comments.

A photograph of your wiring might help us spot the problem.

retronet_RIMBA1ZO


Thanks for you comments.

A photograph of your wiring might help us spot the problem.

It's probably something very basic like wrong breadboard hole, or perhaps a faulty breadboard line ?
I should work through it like a beginner and confirm every connection has continuity ! (I use a multimeter set to buzzer)

If you're willing to take a look at pics, i should be grateful for whatever comments i get.
Looks kind of messy to me - might have to learn to take better pics of breadboards !!



The pic actually shows the setup that works, with the individual lines to GND, but i've also left the 'chain' in there - i suppose that's a no-no if i weren't a beginner... (double connections in parallel means more current flows - have i got that right ?)

retronet_RIMBA1ZO

D'OH !!
absolute n00b error - i didn't even know how to use a breadboard !!
the rails are split halfway on the breadboard.

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